A research team led by scientists from Spain's National Center for Metallurgical Research (CENIM-CSIC) has investigated the erosion resistance of commonly used galvanized coatings in large-scale PV mounting systems.
“While the degradation of PV panels and the corrosion of structural elements are well-studied, limited research has addressed the specific impact of sand erosion on metallic structures in desert and semi-desert environments,” the scientists said. “In these environments, photovoltaic support structures are continuously exposed to wind-driven sand particles. The resulting erosion gradually wears away the protective zinc coatings on galvanized steel. Once this layer is compromised, the underlying steel becomes highly susceptible to corrosion.”
Erosion resistance in PV mounting systems was assessed using two standardized methods: a free-falling sand test and a forced-air sand-impingement test. The study focused on three common galvanized coatings, each with specific applications: continuous galvanized steel (Z275) for torque tubes, Zn-Mg-Al alloy (ZM310) for rafters, and hot-dip galvanized steel (HDG) for piles. These coatings differ in composition and durability, raising considerations about which offers the best balance of performance and longevity under erosive conditions.
All samples were commercial, measuring 10 × 15 cm. An additional sample of aluminum-based motion components with an organic coating was also tested.
In free-falling sand tests, samples were placed at a 45° angle while Ottawa silica sand fell by gravity. HDG, Z275, and ZM310 coatings were tested for 150 cycles, while the organic coating underwent 180 cycles. Each cycle involved 2 L of sand falling at 9,094 g/min, with an estimated impact velocity of 4–5 m/s.
In the forced-air system, silica sand particles were projected onto samples at 45° or 90° angles using a controlled airflow of 0.13 L/s. The impinging velocity was 10 m/s, with mass flow rates of 7 g/min and 15 g/min.
The free-falling sand test showed clear differences in abrasion resistance. The organic coating performed well at 3.75 L/μm, with a slow wear stage of around 7.8 μm/h followed by faster erosion at 33 μm/h. Among galvanized coatings, Z275 eroded slowest (4.03 μm/h), HDG slightly faster (5.52 μm/h), and ZM310 fastest (9.43 μm/h).
In the forced-air test, Z275 again proved most resistant (1.38 ± 0.26 μm/h), ZM310 was less durable (2.47 ± 0.16 μm/h), and HDG showed two-stage erosion, starting at ~1.7 μm/h before rising to 5.7 μm/h. These results suggest that while some coatings maintain steady resistance, others degrade more rapidly under prolonged erosive conditions.
Increasing the severity to 15 g/min significantly increased erosion: Z275 reached 2.78 μm/h at 90° and 4.5 μm/h at 45°, while ZM310 reached 6.9 μm/h at 45°.
“The results indicate that continuously galvanized steel coatings exhibit the lowest erosion rate compared to HDG and Zn-Al-Mg coatings,” the researchers said. “This study also shows that higher hardness does not necessarily improve erosion resistance. The superior performance of Z275 highlights the importance of other factors, including ductility, coating continuity, and resistance to brittle failure, in determining erosion behavior.”
Their findings have appeared in “Surface erosion damage in mounting structures of large-scale photovoltaic systems,” published in Solar Energy Materials and Solar Cells. Researchers from Spain's National Center for Metallurgical Research (CENIM-CSIC), PV solutions specialist Soltec, and Brazil's Federal Center for Technological Education “Celso Suckow da Fonseca” have participated in the study.
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